WO2004012015A1

WO2004012015A1 - Method and device for setting the toner concentration in the developer station of an electrophotographic printer or copier

Info

Publication number: WO2004012015A1
Application number: PCT/EP2003/008056
Authority: WO
Inventors: Alfred Zollner; Bernhard Hochwind; Wolfgang Schullerus; Volkhard Maess; Hans-Detlef Groeger; Peter Möstl
Original assignee: Oce Printing Systems Gmbh
Priority date: 2002-07-24
Filing date: 2003-07-23
Publication date: 2004-02-05
Also published as: DE10233671A1; US7433613B2; EP1525514B1; ATE470174T1; EP1525514A1; US20060269303A1; DE50312775D1

Abstract

The invention relates to a method and device for setting the toner concentration of a toner particle/support particle mixture (26) in a developer station (22), for developing a latent charge of an image on an intermediate support (10) of an electrophotographic printer or copier, whereby a sensor (42), arranged in the developer station (22), measures the toner concentration in the mixture (26). An actuator (40, 42) adjusts the toner supply to the developer station (22). A current usage value (68) for toner particles is determined. A regulator (74) for the regulation of the toner concentration, operates the actuator (40, 42) depending on the signal (50) from the sensor (42) and the determined usage value (68), whereby the toner concentration, at the point of the developer station where the toner is used to develop the latent image, is calculated from the toner concentration measured at the site of installation of the sensor (42) and the usage value (68).

Description

Method and device for adjusting the toner concentration in the developer station of an electrophotographic printer or copier

The present invention relates to a method and an apparatus for adjusting the toner concentration of a toner particle / carrier particle mixture in a developer station of a printer or copier, and an apparatus for developing a latent charge image on an intermediate carrier of an electrophotographic printer or copier.

The toner particles, sometimes also called "toner" in the following, serve to color the latent charge image on the intermediate carrier. In a further step, the toner is then transferred from the intermediate carrier onto a recording medium, e.g. Transfer paper.

Small iron or steel granules are known, for example, as carrier particles. These typically have a two-fold function: on the one hand, the toner particles become triboelectrically charged when the mixture is mixed on the carrier particles, on the other hand the toner particles attach to the carrier particles and are adhered to the intermediate carrier. The transport of the carrier particles to the intermediate carrier is accomplished, for example, with a magnetic developer roller, on which the carrier particles attach. In the immediate vicinity of the intermediate carrier, the electrically charged toner particles are transferred to the intermediate carrier in accordance with the electric field of the charge image, while the carrier particles remain in the developer station or are returned.

During development, toner is thus removed from the developer station by a corresponding supply of toner must be replaced in the developer station. It is necessary both for the quality of the printed image and for the trouble-free operation of the developer station that the toner concentration always corresponds to a predetermined value, hereinafter called the target value.

To set the toner concentration to this setpoint, control methods are usually used in which the current toner concentration, i.e. the actual value (or a variable dependent thereon) is measured and its difference from the target value, the so-called control deviation, is minimized by suitably setting a manipulated variable, for example the supply of toner.

To measure the toner concentration in the developer station, for example, the magnetic permeability of the mixture can be measured with the aid of a sensor, which is characteristic of the toner concentration, since only the carrier particles can be magnetized.

However, for reasons of space, such a sensor cannot be arranged in the section of the developer station from which the toner for developing the charge image is actually removed, as will be explained in more detail below using an exemplary embodiment. Instead, the sensor must be placed in the so-called container of the developer station. This is problematic insofar as a toner concentration gradient arises within the developer station in the printing or copying operation, so that the toner concentration measured in the container deviates from the toner concentration relevant for the printing process in the toner removal area and the control is therefore based on a falsified actual value. Another problem is that the sensor measurement value is influenced by the current toner charge, which changes depending on the toner throughput, among other things. This can also falsify the underlying actual value. These problems are avoided in conventional methods by generating a toner mark on the intermediate carrier instead of directly measuring the toner concentration and then scanning it with a reflected light sensor or the like. This enables a print density to be determined, which in turn is characteristic of the toner concentration.

This method is described for example in DE 101 36 259. A toner mark is generated therein on a photoconductor, the latter being exposed to an intensity at which the print density varies particularly strongly with the toner concentration. In principle, this enables the toner concentration to be determined very precisely, especially since the concentration of the toner is actually recorded in a section of the developer station from which the toner was removed.

However, the toner concentration measurement with the aid of a toner mark is indirect in that the print density of the toner mark depends not only on the toner concentration but also on a number of other variables. These variables include, for example, the illumination intensity of a character generator, the degree of electrostatic charging of the toner, the intensity of the charging of the intermediate carrier and the magnitude of the voltage between the developer roller and the intermediate carrier. The toner concentration can only be reliably determined from the toner mark if all of these variables assume a known, constant value.

However, if one or more of these variables change unnoticed, for example as a result of a defect in the device, the controller of the concentration control is supplied with an incorrect actual value. This can lead, for example, to the fact that toner is continuously supplied to the developer station until it clogs, or that no toner is supplied at all over a longer period of time and the toner concentration drops continuously, which, for example, results in a charge rollover between the intermediate carrier and developer roller can, because the electrical resistance of the mixture decreases as the (electrically non-conductive) toner decreases. In both cases, the developer station can be severely damaged. For reasons of operational safety and controllability of the system, preference is therefore given to a direct concentration measurement.

Another problem with conventional methods for regulating the toner concentration is that the toner concentration is adjusted relatively slowly to the setpoint because the control gain has to be kept relatively low. Too high a control gain leads to unstable control behavior, an increase in susceptibility to interference and poorer management behavior.

DE 199 00 164 AI shows a method and a device for regulating the toner concentration in an electrographic process. Two operating states are provided there. In an operating state, a toner mark is generated on the intermediate carrier, the density of the toner mark is scanned and the toner mark is removed from the intermediate carrier again. The sampled toner density value is used to regulate the toner concentration in the developer station and finds its influence, for example, in a nominal toner concentration value or in a regulating threshold value. In the other operating state, information to be printed is generated on the intermediate carrier as a toner image and is reprinted on a recording medium. In this other operating state, the toner concentration in the developer station is recorded with a toner concentration sensor and attempts are made to maintain a constant toner concentration in the developer station by appropriate subsequent conveying. As an alternative to regulating the toner concentration with the aid of the toner concentration sensor, it is proposed to control the amount of toner supplied by estimating the toner consumption value. DE 196 31 261 AI shows a device for use in an electrophotographic device, with a first control device that uses the blackening of test marks to determine a target value for the toner concentration in a developer station, and a second control device that is arranged downstream of the first control device regulates the toner concentration in the developer station to this setpoint. The second control device has a sensor for determining the toner concentration in the developer station and, depending on the measured toner concentration, generates a toner replenishment signal which can optionally be modified by a signal which corresponds to a toner consumption value.

None of these documents addresses the problem that the toner concentration measured at the installation location of the sensor could deviate from the toner concentration at the location where the toner was removed.

Further related prior art can be found in documents DE 41 37 708 C2, US 5,353,102 and JP 03045973 A.

The invention has for its object to provide a method and an apparatus which enables the development of a latent image with toner with high print quality.

This object is achieved according to the invention by a method with the features of claim 1. In this method, the toner concentration is measured in a mixture with a sensor arranged in the developer station and the toner supply is adjusted with an actuator, a current consumption value for toner particles being determined and a control unit for regulating the toner concentration depending on the signal from the sensor and the actuator controls determined consumption value. The toner concentration in a section of the measured at the installation location of the sensor and the toner consumption value Developer station calculated from which the toner for developing the latent image is removed.

The term "determining" the consumption value is to be understood in a broad sense, meaning both a more or less precise measurement and a mere estimate. Examples of suitable estimates of the consumption value are given below.

Using the determined current consumption value, the errors in the direct measurement can be corrected to a certain extent, since both the spatial concentration gradient in the developer station and the electrostatic charging of the toner are related to the current toner consumption. In particular, the calculated toner concentration at the toner removal location can be entered as a controlled variable in the control unit and the actuator can be controlled by the control unit in such a way that the calculated toner concentration at the toner removal location is approximated to a target value.

Furthermore, the current toner consumption value can be taken into account directly when regulating the toner concentration and not only when it manifests itself in a control deviation. This improves the dynamic behavior of the control.

In the method, the actuator is preferably controlled by the combination of a first and a second manipulated variable, the first manipulated variable being measured according to the toner consumption value and the second manipulated variable based on the measured toner concentration. The first manipulated variable is preferably dimensioned such that it causes a toner supply that corresponds to the current toner consumption value. In this case, the current consumption value represents a disturbance variable that counteracts the first manipulated variable directly and without feedback. The second manipulated variable is preferred dimensioned so that it regulates the toner concentration to a target value.

In the simplest case, the "combination" of the two manipulated variables is simply an addition of the two. For example, the first manipulated variable can be the output signal of a control chain, which is added to the signal of the second manipulated variable, which in turn is formed by the output signal of a control loop. However, it is just as well conceivable, for example, that the consumption value is converted into an auxiliary variable which is fed into the controller and is dimensioned such that it produces a manipulated variable which corresponds to a toner supply in accordance with the consumption value. If a control deviation and this auxiliary variable are now fed into the controller at the same time, the controller outputs a manipulated variable which is referred to here as a "combination" of two manipulated variables, namely a first manipulated variable which would result if only the auxiliary variable were fed into the controller would be fed, and a second manipulated variable, which would result if only the control deviation were fed into the controller. Depending on the type of controller, this combination of the first and second manipulated variable is not necessarily a sum, but a function of the two. In this generality, the term “combination” of the two manipulated variables is to be understood in the present invention.

In an advantageous embodiment of the method, the toner supply set on the actuator is assumed to be the toner consumption value. This choice of the estimated value results from the following consideration: If the method works as desired, the current toner concentration corresponds to its target value and the current toner supply corresponds to the current toner consumption. In this case, the current toner supply is a very good estimate of the current toner consumption. In this respect, the choice of the estimated value is self-consistent: the better the method works, the better the estimated value of the toner consumption, on the basis of which the method then works again works better. It has been shown that despite the implicit feedback, a stable control behavior can be obtained through a suitable choice of control parameters. The advantage of this special embodiment of the method is that the current toner supply is a quantity that is easy to grasp, so that this method can be used in conventional devices without major structural interventions.

In a particularly advantageous development of the method according to the invention, the toner consumption value is estimated from print data. The toner consumption value is preferably estimated from the number of pixels to be printed, weighted with its inking level. Such an estimate of the toner consumption value is already known from US Pat. No. 5,202,769, but is only used therein for the pure control of the toner supply, but not in the context of a regulation. However, mere control is unsuitable to set the toner concentration stable and safe over a long period of time, because small systematic deviations between actual and estimated toner consumption add up over time. In the event of malfunctions in the printing or copying process, the deviation from the actual and estimated toner consumption can become very large, so that a toner concentration in the developer station that is much too high or too low quickly arises, which, as mentioned above, can damage it.

In practice, the toner consumption value can be estimated from the print data so precisely that the first manipulated variable, which is based on the toner consumption value, already causes a toner concentration in the developer station that is close to the target value for short and medium times. The second manipulated variable then causes only a relatively slight correction of the toner supply which is controlled by the first manipulated variable. Overall, the control dynamics are greatly improved because the pre-controlled portion of the toner supply, that is to say the first manipulated variable, reacts immediately to the determined toner consumption value and the second manipulated variable has to compensate for far fewer control deviations than in a conventional method.

Since the print data in a printer or copier are processed in a control unit, this must be modified in order to implement the latter method in conventional devices. If this is to be avoided, for example for reasons of cost or to maintain the continuity of a product range, the toner consumption value can be estimated in an alternative development of the method from the number of pixels, weighted with its coloring level, which are set in the character generator producing the latent printed image. In this case, the pixels are preferably counted with the aid of an application-specific integrated circuit which is connected to the character generator. This solution therefore requires only a relatively small addition, but not a substantial modification of a conventional printer or copier system.

In a further alternative development, the toner consumption value is estimated on the basis of the current consumption of the character generator generating the latent charge image. This is possible because the toner consumption and the power consumption in the character generator are directly related. A certain amount of light energy is required to generate each pixel of the charge image, which in turn is reflected in the power consumption of the character generator. In practice, a toner consumption value that is sufficiently good for the purposes of the method according to the invention can be estimated from the power consumption. The advantage of this further developed method is that it can be implemented in existing printer and copier systems with minimal structural additions. In the context of the described method, the toner consumption value can be determined “in advance” for practical reasons. This is the case, for example, in the above-mentioned development, in which the consumption value is estimated from pressure data which are usually already present a certain time before the charge image is developed. In such a case, the determined toner consumption value is preferably stored in a data buffer, for example a delay buffer, until the corresponding printed image is colored. Then the control unit for controlling the toner concentration can control the actuator depending on the determined consumption value at exactly the point in time at which the determined consumption actually takes place, which improves the control dynamics.

In an advantageous development, the relative weighting of the first and second manipulated variable is varied in the course of the printing or copying process. The second manipulated variable is preferably suppressed in the starting phase of a printing or copying process and its weighting is increased when the state of the mixture in the developer station has stabilized. Because in the start-up phase, the toner concentration in the developer station can only be determined inaccurately, since the mixture run has not yet stabilized. Due to the imprecise concentration measurement in the start phase, it is advisable to rely on the first manipulated variable first.

The controller unit preferably comprises a PID controller. In an advantageous development, the control parameters used are varied in the course of the printing or copying process.

For a better understanding of the present invention, reference is made below to the exemplary embodiments illustrated in the drawings, which are described using specific terminology. However, it should be noted that the scope of protection of the invention is not to be restricted thereby, since such modifications and further modifications to the devices and methods shown and such further _. Applications of the invention as set forth therein are considered to be the present or future expertise of a person skilled in the art. The figures show exemplary embodiments of the invention, namely

FIG. 1 shows a schematic drawing of components of an electrophotographic printer,

FIG. 2 shows a schematic illustration of a developer station with toner supply and control unit,

FIG. 3 shows a block diagram in which a conventional control method is shown,

FIG. 4 shows a schematic representation of a developer station, in which the location dependence of the toner concentration is shown as a model,

FIG. 5 shows a schematic diagram of the toner concentration distribution in a developer station in a conventional control method,

FIG. 6 shows a schematic diagram of the toner concentration distribution in a developer station in the control method according to the invention,

Figures 7 to 9

Block diagrams of three embodiments of the method according to the invention,

FIG. 10 shows the schematic structure of a control unit, FIG. 11 shows the schematic structure of a further control unit,

FIG. 12 four schematic diagrams a-d, in which the determined toner consumption value (a), the actual one

Toner consumption (b), the control value for the toner supply (c) and the toner concentration (d) have occurred over time, and

Figures 13 to 15

Block diagrams in which further developments of the method according to the invention are shown schematically.

The basic features of electrophotographic printing or copying are briefly explained below with reference to FIG. 1. In Figure 1, a photoconductor drum 10 is shown in cross section, the peripheral surface of which is coated with a photo semiconductor, for example arsenic triselenide (As ₂ Se ₃ ). Such a photo semiconductor has a high dark resistance, which, however, drops with sufficient exposure. The photoconductor drum 10 rotates in the direction indicated by the arrow 12. Her photo semiconductor layer is first electrostatically charged with the help of a so-called charging corotron 14. By rotating the photoconductor drum 12, the charged section arrives at a character generator 16 with a light source 18 (an LED comb in FIG. 1) and a control unit 20. The control unit 20 specifies at which points the photoconductor drum 10 is to be exposed. At the exposed areas, the electrical resistance of the photo semiconductor layer drops and the charge flows off. In this way, pixels of a latent charge image are generated on the photoconductor drum. These pixels, called pixels, are therefore "set" in the character generator.

Upon further rotation of the photoconductor drum 10, the latent charge image reaches a developer unit 22 Developer unit 22 comprises a container 24 in which there is a mixture 26 of toner particles and carrier particles. In the developer station shown, the carrier particles consist of a magnetic material such as iron or steel and ferrite. Therefore, the carrier particles can be attracted to a magnetic developer roller 28 and conveyed to the photoconductor drum 10 together with the toner particles adhered to them by rotating the developer roller 28. The carrier particles align themselves along the magnetic field lines generated by the developer roller 28 in such a way that they form a brush-like arrangement on the surface of the developer roller 28, which is referred to as a "magnetic brush" 56 (cf. FIG. 4).

The toner particles are charged in the developer ^* station 22 triboe- lectric and transmitted with the aid of a suitable electric field of the magnetic brush 56 on the exposed (so-called "dark letter") unexposed areas of the photo-semiconductor (so-called "Light-writing") or. Thus, the charge image located on the photoconductor drum 10 is colored with toner, ie developed.

The toner image is then transferred to a printing medium, for example a sheet of paper 32, in a transfer printing station 30. Therefore, the photoconductor drum 10 is generally referred to as an intermediate carrier.

Any toner remaining on the photoconductor drum 10 during transfer printing is finally removed with the aid of a cleaning device 34.

The developer station 22 is shown enlarged in FIG. Since only toner, but no carrier particles, are transferred to the photo semiconductor layer during the development of the latent charge image, the toner concentration in the container 24 of the developer station 22 would decrease over time if toner was not continuously added to the developer station 22. would lead. The developer station 22 is therefore connected to a toner reservoir 36, and the toner supply from the reservoir 36 into the developer station 22 takes place with the aid of a motor 38 which drives a conveying device.

The delivery rate of the motor 38 is predetermined by a motor controller 40. A common method of adjusting the toner concentration in developer station 22 is based on a simple control loop. The current toner concentration in the developer station 22 is measured with the aid of a sensor 42. The measured toner concentration is the controlled variable 44, which represents the input signal to a controller 46. The control deviation is calculated in the controller 46 by subtracting the controlled variable 44 from a reference variable. The controlled variable is called the actual value, the reference variable is called the setpoint. From the system deviation, the controller 46 generates a manipulated variable 48 that is sent to an actuator, which in the present case is formed by the motor 38 and the motor controller 40. The manipulated variable 48 is dimensioned such that it causes a toner supply via motor control 40 and motor 38, which compensates for the control deviation. It should be noted that here and in the following terms such as controlled variable 44 and manipulated variable 40 are used both for the abstract elements of the control loop and for the signals which transmit the corresponding variables.

The essential elements of this conventional control method are summarized in a block diagram in FIG. In addition to the elements and signals discussed in connection with FIG. 2, FIG. 3 shows a measurement value acquisition device 52 which, on the basis of a sensor signal 50 from the sensor 42, generates the controlled variable 44 and a motor signal 54 with which the motor controller 40 uses the motor 38 controls. The motor can be operated intermittently or the speed can be varied. However, this conventional control method shown in FIG. 3 has several problems. The first problem is that the toner concentration measured with the aid of the sensor 42 does not necessarily correspond to the toner concentration at the location at which the toner is actually removed for developing the photoconductor 10. The problem is shown schematically in FIG. 4, in which the brightness of the toner-carrier particle mixture 26 represents the toner concentration as a model. The toner concentration is particularly high in the area labeled A in which toner is supplied, and in the area labeled C from which toner is removed for development. This toner concentration gradient occurs even though the mixture 26 is mixed in the developer station, for example with the aid of a paddle wheel (not shown). The term "slope" is not intended to mean that the toner concentration changes linearly with location. In fact, there may be a general, non-linear relationship between toner concentration and location.

The concentration that is essential for the printing or copying process is that in the toner removal area C. However, no sensor can be installed in the toner removal area C, because this would get in the way of the developer roller 28 and the structure of the magnetic brush 56. Instead, the sensor must be arranged at a location B in the container 24 of the developer unit 22 at which the current toner concentration usually does not match that in the toner removal area C.

The toner concentration gradient is shown schematically in the diagram in FIG. Therein, the graph 58 shows the toner concentration (TK) dependent on the position P in the developer station 22 with low toner consumption, ie low toner extraction per unit of time. As can be seen in FIG. 5, the toner concentration in the entire developer station is almost identical. This is because with low toner consumption there is enough time for the to- balances by mixing the toner carrier particle mixture.

The • Graph 60 shows the spatial toner concentration distribution with high toner consumption. 5, there is a considerable drop in the toner concentration within the developer station 22. If, as shown in FIG. 5, the toner concentration at the installation location B of the sensor is regulated to its target value (S), the toner concentration in the removal area C is clearly below the target value. This leads to poor printing behavior and, in the worst case, to damage to the developer station 22. FIG. 5 is only to be understood schematically. For the sake of simplicity, a linear course of the toner concentration as a function of the position has been assumed, but a more complicated dependence is also possible.

Since the gradient of the toner concentration in the developer station 22 depends on the current toner consumption, the method according to the invention provides for determining a current toner consumption value more or less precisely, and from this together with the toner concentration measured at the installation location B of the sensor, the toner concentration in the removal area C. to calculate. Then the toner concentration at the installation location B of the sensor is set so that the (calculated) toner concentration in the removal area C corresponds to the target value.

The toner concentration distribution thus effected is shown as graph 62 in FIG. 6. The difference between the toner concentration actually set at location B and the target value (S) is called sensor correction 64. As said, the sensor correction 64 is a variable that is calculated from the determined toner consumption value.

The “calculation” of the toner concentration in the removal area C is typically carried out by means of a simulation. The simulation is thereby a model for the relationship between the to- nerkonzentration at the removal location C, the toner concentration at location B of the sensor 42 and the toner consumption value. The model and its model parameters can be determined empirically by adapting to test measurements.

In experiments, the inventors found that the toner concentration TK (C) at the removal location C can already be simulated very precisely as follows using a simple, linear model of the toner concentration at the installation location of the sensor TK (B) and the toner consumption value,

TK (C) = TK (B) - α • Toner consumption value.

There is an empirically determined proportionality constant. This simulation model can, for example, be supplemented by higher-order terms in the toner consumption value, the coefficients of which can be determined by adapting to experimentally determined data.

In the following, several options are proposed for determining the current toner consumption value. It is clear that "determining" in this context cannot mean exact recording of the actual current toner consumption, because if this were possible, the task of the entire method would already have been achieved. In the context of the present invention, “determining” means any direct or indirect approximate determination of the current toner consumption, including its estimation.

When the control loop is steady, the manipulated variable 48 is already a relatively good estimate of the current toner consumption. As shown in FIG. 7, in one embodiment of the method according to the invention, the manipulated variable 48 is entered as the current toner consumption value in a correction unit 66, which determines the sensor correction 64 therefrom and which sends a corresponding sensor correction signal to the measuring device 52. Again, neither language nor borrowed with respect to the reference number between the sensor correction and the corresponding signal.

The use of the manipulated variable 48 as a toner consumption value represents a feedback that could in principle bring the control loop out of balance. However, it has been shown in practice that this feedback can also achieve stable control behavior if the control parameters are selected appropriately.

In another embodiment of the method according to the invention shown in FIG. 8, the toner consumption value 68 is determined in a printer controller 70 on the basis of print data and transmitted to the correction unit 66. The consumption value 68 can be calculated in the printer controller during or after the preparation of the print data. In the exemplary embodiment of the method according to the invention shown, the number of pixels to be inked is determined from the print image data for each of a certain number of inking stages, and the toner consumption is estimated therefrom. Specifically, this is done as follows: each pixel to be printed is assigned to one of m inking levels (gray levels), where m is a natural number. If the number of pixels of the i-th coloration level is denoted by n _±, the estimated value for the toner consumption is calculated according to:

Toner consumption = k _Ve rb ^• (ki • ni + ... 4- ki ^■ ni +... + K _m • n _m ) + k ₀ ,

where ki is the weighting factor of the number of pixels of the i-th coloration level and k _Ve rb is a proportionality factor. k ₀ Designates a basic consumption of toner due to dust formation, suction or the like

The print image data is processed in the printer controller 70 before the exposure and inking of the photo semiconductor of the photo drum 10. There can be a certain, not insignificant period of time between the preparation of the print data and the development of the photoconductor. Therefore in the representation of 8, a delay buffer 72 is provided, in which the toner consumption value determined by the printer controller 70 is temporarily stored for the duration of this period and is only passed on to the correction unit 66 when the image corresponding to the print data is actually developed.

In addition to the inhomogeneous toner concentration distribution in the developer station 22 described above, there is another source of error that can falsify the concentration measurement. This is because the measured value of the sensor 42 is influenced by the size of the electrostatic charge on the toner, which in turn is subject to fluctuations. However, the state of charge of the toner is also dependent on the toner throughput, i.e. depending on toner consumption. Therefore, a measurement value that is falsified due to a toner charge that deviates from the target value can also be corrected by the correction unit 66 using the current toner consumption value 68.

Another problem of the control method of FIG. 3 and also of the improved control method of FIGS. 7 and 8 is that the control dynamics that can be achieved with it are relatively sluggish. This means, for example, that a certain lack of toner must first occur until the controller 46 begins to supply the missing amount of toner via the motor control 40 and motor 38. The reason for this is that the control gain of the controller 46 cannot be chosen to be arbitrarily large, because otherwise the control loop would be susceptible to failure. As a consequence, in the conventional control method, a toner concentration occurs again and again in the developer station 22, which deviates considerably from the target value, which affects the print quality and, in the worst case, can damage the developer unit 22.

A solution to this problem is shown in Figure 9. Instead of the controller 46 according to FIGS. 3, 7 and 8 occurs in FIG. 9 shows a controller unit 74 which, in addition to the input for the controlled variable 44, has an input for the determined toner consumption value 68. The control unit 74 generates a combined manipulated variable 76 from the controlled variable 44 and the toner consumption value 68. The combined manipulated variable 76 is composed of a first manipulated variable, which is a purely control variable and causes a toner supply that corresponds to the toner consumption value 68, and a second manipulated variable, which is measured from the controlled variable 44 and essentially corresponds to the manipulated variable 48 in the conventional method of FIGS. 3, 7 and 8. As a result, the toner supply is precontrolled in a certain sense by the determined toner consumption value 68. The second manipulated variable basically serves to compensate for errors in the pilot control by means of regulation.

When using the method of FIG. 9, there are far fewer control deviations than in the conventional method, i.e. Due to the precontrol, the controlled variable 44, that is to say the actual value of the toner concentration, is relatively close to its target value. Since a change in the toner consumption is counteracted directly via the first manipulated variable, the dynamic behavior of the toner concentration setting according to FIG. 9 is far better than in the conventional, pure control method.

As stated, the first manipulated variable is the manipulated variable that the control unit 74 would output if the control deviation were zero and only a certain toner consumption value signal 68 was fed into the control unit 74. The second manipulated variable is the manipulated variable which the control unit 74 would output if only the controlled variable 44, ie a measured value of the target concentration were fed into the control unit 74, but no toner consumption value signal 68 was present at the control unit 74. How these two manipulated variables are combined to form a manipulated variable 76 depends on the special structure of the control unit 74. All control units 74 in which the controlled variable 44 (the measured toner concentration) and the determined toner consumption value 68 are processed to a common manipulated variable 76. Without limitation, however, two simple examples for the controller unit 74 are to be explained in FIGS. 10 and 11 for illustration.

An exemplary embodiment for the control unit 74 is shown in FIG. The control unit 74 comprises a controller 46 of essentially the same type as in FIGS. 2, 3, 7 and 8. The controller 46 receives the controlled variable 44 as an input signal and outputs the second manipulated variable 78 as an output signal. The controller 74 further comprises a control element 80 which generates the first manipulated variable 82 from the toner consumption value 68. In node 83, the first manipulated variable 82 and the second manipulated variable 78 are added to the combined manipulated variable 76.

In the example of FIG. 11, the control unit 74 comprises, in addition to the controller 46, a control unit 84 which generates an auxiliary variable 86 from the toner consumption value 68, which is added to the control variable 44. The auxiliary variable 86 corresponds to that hypothetical control deviation from which the controller 46 would prescribe a toner supply corresponding to the toner consumption value 68. In contrast to the exemplary embodiment in FIG. 10, the first and second manipulated variables do not occur explicitly in the control unit 74 in FIG. 11, but according to what has been said above, they are already determined by the signals present, i.e. the toner consumption value 68 or the controlled variable 44 are well defined and are reflected in the combined manipulated variable 76. In this broad sense, the term “combination of the first and second manipulated variable” is to be understood in the context of the present invention.

FIG. 12 shows the determined toner consumption value TVE (a), the actual toner consumption TV (b), the manipulated variable SW2 of the second manipulated variable or the manipulated variable SWK of the combined manipulated variable (c) and the actual value I of the toner concentration (d) in a schematic diagram against a common time axis applied. The toner consumption value 68 entered in diagram (a) has been determined in the printer controller 70 of FIGS. 8 and 9 from print data. Since the print data are available before the charge image is developed, the determined toner consumption value is also available in each case by a time interval T before the actual toner consumption. For this time interval T, the toner consumption value 68 is temporarily stored in the delay buffer 72 (see FIGS. 8 and 9) and is therefore synchronized with the actual toner consumption, as shown in diagram (b).

Diagram (b) shows that the determined toner consumption value 68 (solid line) deviates somewhat from the actual consumption TV (dotted line). In the time interval Ti, the determined toner consumption value 68 is, for example, above the actual consumption TV. Furthermore, the control deviation at the beginning of the interval Ti is 0, as can be seen in diagram (d), and the manipulated variable SW2 of the second manipulated variable is therefore initially also equal to 0 (see diagram c). The manipulated variable SWK of the combined manipulated variable at the beginning of the interval Ti therefore only results from the first manipulated variable and, as can be seen in diagram (c), is above the actual consumption because the determined consumption value was overestimated. As a result, the actual value of the toner concentration at the beginning of the interval Ti rises above the target value.

In response to this control deviation, the control unit 74 generates a second manipulated variable with a negative manipulated variable SW2, which corrects the manipulated variable SWK of the combined manipulated variable and adjusts it to the actual toner consumption TV approximately at the middle of the time interval Ti (see diagram (c)). The same behavior is shown in the time intervals T ₂ and T ₃ , in which the determined toner consumption value 68 is also above the actual toner consumption. In the interval T ₄ , the determined toner consumption value 68 lies below the actual toner consumption TV, so that the manipulated variable SWK of the combined manipulated variable SWK is initially below the actual toner consumption TV due to a too small first manipulated variable. As a result, the actual value I of the toner concentration TK initially falls below the setpoint S, but is then regulated back to the setpoint S by a then positive manipulated variable SW2 of the second manipulated variable.

It is clear from diagram (c) in FIG. 12 that the second manipulated variable only makes a relatively small contribution to the combined manipulated variable. It essentially serves to correct errors in the first manipulated variable due to an inaccurate estimated value. Since the first manipulated variable immediately reacts to a determined change in the toner consumption value, the dynamics of the method according to the invention for setting the toner concentration are very good. In contrast to a pure control method, in the method according to the invention a systematic error in the determination of the toner consumption value is corrected, which would otherwise add up over time and would lead to a divergent toner concentration in the developer station 22.

FIG. 13 shows an alternative embodiment of the method according to the invention, which differs from the method of FIG. 9 in the way in which the toner consumption value 68 is determined. For this purpose, in the method of FIG. 13, a pixel counter 88 is used, which counts the pixels set for each coloring step in the character generator 16 (see FIG. 1). In the exemplary embodiment shown, the pixel counter 88 is formed by an application-specific integrated circuit (ASIC). The pixel counter 88 has three inputs 90, 92 and 94 corresponding to the three coloring levels, light gray, dark gray and black, which are taken into account in the present exemplary embodiment. For each pixel that is set in the character generator 16, a signal in the coloration level of the pixel is corresponding input 90, 92 or 94 fed. In the pixel counter 88, the toner consumption value 68 is determined from the counted pixels by weighting with their respective inking level in a manner similar to that already described above. Such a pixel counter 88 can be easily combined with conventional systems without having to be significantly modified. The pixel counter 88 may be provided with a delay buffer 72 similar to the printer earth controller 70 of FIG. 8.

FIG. 14 shows a particularly simple and inexpensive implementation of the method according to the invention. The electrical current with which a current source 96 supplies the character generator 16 is measured in a current measuring device 98 and the measured value is transferred to a toner consumption estimator 100. The toner consumption estimator 100 estimates the toner consumption value 68 from the power consumption of the character generator 16. This succeeds because the power consumption of the character generator 16, as already explained above, is a measure of the number and coloration level of printed pixels. The advantage of the method in FIG. 14 is that it can be implemented in conventional printers or copiers with very little design effort.

An advantageous development of the method according to the invention is outlined in a block diagram in FIG. In this method, the contributions of the first and second manipulated variables to the combined manipulated variable 76 are varied over time. A signal weight 102, which determines the weight with which the controlled variable 44 is to be taken into account when generating the combined signal 76, and a signal weight 104, which determines the weight with which the determined consumption value 68 in the combined manipulated variable 76 is used, serve for this purpose To find precipitation.

The corresponding weighting can be specified according to FIG. 15 via time-dependent weighting functions fl (t) and f3 (t). For example, the controlled variable 44 is not very reliable in the starting phase of a printer or copier because the mixture flow in the developer station 22 has not yet stabilized. It is therefore advantageous to keep the contribution of the controlled variable 44 to the combined manipulated variable 76, ie the weight of the second manipulated variable with the aid of the signal weight 102 and a suitable choice of fl (t) in the start phase, and to increase it only when the state changes of the mixture in the developer station 22 has stabilized.

In addition, different control parameters are suitable for use in the controller 46 for different time sections of the printing or copying process or for different states of the printer or copier, such as, for example, warm-up phase, print phase, calibration phase, freshness of the toner, etc. Therefore, the control unit 74 in the exemplary embodiment 15 shows a memory 106 in which the control parameters are stored in accordance with a time-dependent or state-dependent function f2 (t).

In the exemplary embodiments shown, the controller 46 is a PID controller, therefore the function f2 (t) is a vector-valued function, the vector components of which contain all the required control parameters. A toner consumption estimator, which is not specified in more detail and which determines the consumption value 68, is designated by 108 in FIG. The previously described elements of printer controller 70, pixel counter 88 or toner consumption estimator 100 can be used as toner consumption estimators 108.

Although preferred exemplary embodiments have been shown and described in detail in the drawings and in the preceding description, this should be regarded as purely exemplary and not as limiting the invention. It is pointed out that only the preferred exemplary embodiments are shown and described, and all of them Changes and modifications that are presently and in the future within the scope of the invention are to be protected.

LIST OF REFERENCE NUMBERS

10 photoconductor drum

12 direction of rotation of the photoconductor drum 10

14 charging corotron. 16 character generator

18 LED comb

20 control unit

22 developer station

24 container 26 toner particle-carrier particle mixture

28 developer roller

30 transfer station

32 paper

34 cleaning device 36 toner reservoir

38 engine

40 engine control

42 sensor

44 controlled variable 46 controller

48 manipulated variable

50 sensor signal

52 Data acquisition

54 Motor signal 56 Magnetic brush

58 toner concentration distribution (low consumption)

60 toner concentration distribution (high consumption)

62 toner concentration distribution (high consumption)

64 Sensor correction 66 Correction unit

68 determined toner consumption value

70 Printer control

72 delay buffers

74 Control unit 78 second manipulated variable

80 control

82 first manipulated variable 83 node

84 control

86 auxiliary size

88 pixel counters

90 entrance

92 entrance

94 entrance

96 power source

98 current measuring device

100 toner usage estimates

102 signal weights

104 signal weights

106 memories

108 Toner Consumption Estimator

Claims

Expectations

1. A method for adjusting the toner concentration of a toner particle-carrier particle mixture (26) in one

Developer station (22) for developing a latent charge image on an intermediate carrier (10) of an electrographic printer or copier, in which

a sensor (42) arranged in the developer station (22) measures the toner concentration in the mixture (26),

an actuator (40, 42) stops supplying toner to the developer station (22),

a current consumption value (68) for toner particles is determined, and

in which a control unit (74) for controlling the toner concentration controls the actuator (40, 42) depending on the signal (50) from the sensor (42) and the determined consumption value (68),

wherein from the toner concentration measured at the installation location (B) of the sensor (42) and the toner consumption value (68), the toner concentration at a location (C) deviating from the installation location is calculated in the developer station, at which the toner for developing the latent image is removed becomes.

2. The method according to claim 1, wherein the calculated toner concentration at the toner removal location (C) is entered as a controlled variable in the control unit (74) and the control unit (74) controls the actuator (40, 42) in such a way that the calculated toner concentration at the toner removal location ( C) is approximated to a target value.

3. The method according to claim 1 or 2, in which the consumption value (68) is estimated.

4. The method according to any one of claims 1 to 3, wherein the actuator (38, 40) by the combination of a first

Control variable (82) and a second control variable (78) is controlled, the first control variable (82) based on the toner consumption value (68) and the second control variable (78) according to the measured toner concentration.

5. The method of claim 4, wherein the actuator 38, 40) is controlled by the sum of a first manipulated variable (82) and a second manipulated variable (78), the first manipulated variable (82) according to the toner consumption value (68) and the second manipulated variable (78) measured according to the measured toner concentration.

6. The method of claim 4 or 5, wherein the first manipulated variable (82) is dimensioned so that it causes a toner supply which corresponds to the current toner consumption value (68).

7. The method of claim 4, 5 or 6, wherein the second manipulated variable (78) is dimensioned so that it regulates the toner concentration to a target value.

8. The method according to any one of the preceding claims, wherein the toner supply set on the actuator (38, 40) is assumed to be the toner consumption value (68).

9. The method according to any one of claims 1 to 7, wherein the toner consumption value (68) is estimated from print data.

10. The method of claim 9, wherein the toner consumption value (68) is estimated from the number of pixels to be printed weighted with its inking level.

11. The method according to any one of claims 1 to 7, in which the toner consumption value (68) is estimated from the number of pixels weighted with its inking level, which are set in the character generator (16) producing the latent printed image.

12. The method of claim 11, wherein the pixels are counted using an application specific integrated circuit (88) connected to the character generator (16).

13. The method according to any one of claims 1 to 7, wherein the toner consumption value (68) is estimated on the basis of the current consumption of the character generator (16) generating the latent charge image.

14. The method according to any one of claims 9 to 13, in which the determined toner consumption value (68) is stored in a data buffer (72) until the corresponding print image is colored.

15. The method according to any one of claims 4 to 14, wherein the relative weighting of the first and second manipulated variable (82, 78) is varied in the course of the printing or copying process.

16. The method according to claim 15, wherein the second manipulated variable (78) is suppressed in the start phase of a printing or copying process and its weighting is increased when the state of the mixture (26) has stabilized in the developer station.

17. The method according to any one of the preceding claims, wherein the control unit (74) comprises a PID controller (46).

18. The method according to any one of the preceding claims, wherein the control parameters used by the control unit are varied in the course of the printing or copying process.

19. Device for developing a latent charge image on an intermediate carrier of an electrographic printer or copier

a developer station (22) in which a toner particle-carrier particle mixture (26) is located,

a sensor (42) arranged in the developer station (22) for measuring the toner concentration in the mixture (26),

an actuator (38, 40) for adjusting the toner supply to the developer station (22),

Means (70, 88, 100) for determining a current consumption value (68) for toner particles and

a control unit (74) which controls the actuator (38, 40) depending on the signal (50) from the sensor (42) and the determined toner consumption value (68) to regulate the toner concentration, in which means (66) are also provided, use the toner concentration measured at the installation location (B) of the sensor (42) and the toner consumption value (68) to calculate the toner concentration at a location (C) in the developer station that is different from the installation location, from which the toner for developing the latent image is removed ,

20. The apparatus of claim 19, wherein the calculated toner concentration at the toner removal location (C) can be entered as a control variable in the control unit (74) and the control unit (74) is designed such that it controls the actuator (40, 42) in this way that the calculated toner con concentration at the toner removal location (C) is approximated to a target value.

21. The apparatus of claim 19 or 20, ^' in which the actuator (38, 40) is controlled by the combination of a first manipulated variable (82) and a second manipulated variable (78), the first manipulated variable (82) being based on the toner consumption value ( 68) and the second manipulated variable (78) according to the measured toner concentration.

22. The apparatus of claim 21, wherein the first manipulated variable (82) is dimensioned such that it causes a toner supply that corresponds to the current toner consumption value (68).

23. The apparatus of claim 21 or 22, wherein the second manipulated variable (78) is dimensioned such that it regulates the toner concentration to a desired value.

24. The device according to one of claims 19 to 23, wherein the toner consumption value (68) is estimated from print data.

25. The apparatus of claim 24, wherein the toner consumption value (68) is estimated from the number of pixels to be printed weighted with its inking level.

26. Device according to one of claims 19 to 23, in which the toner consumption value (68) is estimated from the number of pixels weighted with its inking level, which are set in the character generator (16) producing the latent printed image.

27. The apparatus of claim 26 with an application-specific integrated circuit (88) connected to the character generator (16) for counting the pixels.

8. Device according to one of claims 19 to 23 with a current measuring device 98 for measuring the current consumption of the character generator (16) generating the latent charge image and means (100) for estimating the toner consumption value (68) based on the power consumption of the character generator (16).